Cable modems are being deployed today that allow high-speed Internet access in the home over a cable network, often referred to as a hybrid fiber copper (HFC) cable network. A functional block diagram of a cable modem 12 in use in a cable network 10 is shown in FIG. 1. Cable modems (CM) 12 are units, often referred to as consumer premise equipment (CPE), that are connected to a personal computer (PC) or other computing device, for example. A cable modem 12 is adapted to communicate with the cable modem termination system (CMTS) that is typically located at a cable network provider's headend 14. The cable modem 12 typically includes some networking layers, a physical (PHY) layer (modulator/demodulator), a Media Access Control (MAC) (e.g. a Data Over Cable System Interface Specification (DOCSIS) MAC), and it may include upper networking layers. The CM is used to receive Internet traffic or information, data, and telephony. All of the information to the CM is transferred through the CMTS. Using a cable modem 12 over a cable network 10 provides a much faster connection, being at least 10 times faster than a 56K modem, for example.
A cable modem 12 performs modulation and demodulation and the operations necessary to interface with a PC. A cable modem 12 typically comprises a transmitter for upstream modulation of a data signal, usually in short bursts, to a receiver in the headend 14 that serves as an upstream demodulator. The upstream direction refers to sending a data signal from the user at the cable modem 12 towards the headend 14. The upstream signal typically comprises Internet data request information or Voice Over IP telephony, for example, and may be a QPSK/16-QAM at 10 Mbit/s. Cable modem 12 also comprises a receiver for downstream demodulation of signals received from a transmitter in the headend 14 that serves as a downstream modulator. The downstream direction refers to sending a data signal from the headend 14 to the cable modem 12. The downstream modulation/demodulation may be 64-QAM/256 QAM at 27–56 Mbit/s, for example. Both the cable modem 12 and headend 14 include MACs, not shown, that control the media access control (MAC) sublayer of the communication network.
A recent development in cable TV network is the addition of a fiber node 16 coupled between the central office headend 14 and the cable modems 12 in users' homes, as shown in FIG. 1. The fiber node 16 may comprise a fiber node such as AT&T's mini fiber node (mFN) and may be adapted to service around fifty homes or users. A fiber node 16 increases network capacity and reliability, and reduces operating costs, by reducing active components on the final coaxial run to the home.
FIG. 2 shows a more detailed block diagram of a typical architecture of a cable network 10. The national Internet backbone 18 is coupled to the central office headend 14. Headend (HE) 14 is coupled to primary hubs (PH) 20 configured in a primary ring arrangement. Each primary hub 20 is coupled to a plurality of secondary hubs (SH) 22, each secondary hub 22 adapted to service a plurality of households, e.g., 20,000 household passed (HHP). Secondary hubs 22 are coupled to a plurality of mux nodes (M×N) 24, with each mux node 24 adapted to service a plurality of households, e.g., 500 HHP. Each mux node 24 is coupled to a fiber node 16 that may have a backup, with each fiber node 16 adapted to service 50 HHP, for example. Each fiber node (FN) 16 is coupled to and provides cable service to a plurality of cable modems (CM) 12.
The communications over network 10 typically are in accordance with an Internet protocol (IP)/Ethernet standard. The communications from fiber nodes 16 to cable modems 12 is typically in accordance to DOCSIS standard via coax cables. To simplify the fiber node 16 complexity, some of the functionality of the DOCSIS control may be transferred to the secondary hub 22. The connection between the headend 14 through to the fiber nodes 16 is typically via fiber using, for example, Native IP over fiber, IP over Sonet, or IP over SDH.
The present invention relates to a novel design and architecture of a cable network communications device.